Connective tissue is the main determinant of the mechanical properties of the lungs and is also thought to play a role in the exchange of nutrients and metabolites between the capillary and epithelial cells and in the diffusion of O2 and CO2 between the alveolar gas and the blood. Although proteoglycans represent only a small portion of the connective tissue of lung parenchyma, they are thought to play an important role in the maintenance of the structural integrity of the tissue, perhaps through their interactions with collagen and elastin. This research project is designed to: 1. find efficient methods for the isolation and purification of the proteoglycans of animal lung parenchyma. This objective has largely been accomplished. 2. characterize the isolated proteoglycans by chemical, physical and immunological methods. 3. identify the portion of proteoglycans resisting extraction. 4. study possible interactions between lung proteoglycans and collagen. Animal lungs are used in this project since they can easily be obtained in large amounts. The ultimate goal is to apply the knowledge thus gained to the study of human lungs, both normal and diseased (particularly emphysematous).